Modern vehicles are increasingly becoming equipped with active safety systems such as collision warning systems, lane keeping assistance, and automated braking. Also systems that perform automated steering in order to avoid collisions have been suggested. A problem related to active safety systems that intervenes the driver, either only via sending an alarm signal to the driver, or via intervention in the command over the vehicle, is that any unnecessary intervention by the active safety system reduces the driving comfort and may become annoying to the driver. A driver may find a vehicle equipped with such a system unreliable. A further problem related to active safety systems is to decide when to intervene. If intervention is made early, intervention may be made by use of small corrections as regards braking effect or yaw angle correction. However, for early interventions predictions of the paths of external objects must be performed for a longer period of time, which decreases the accuracy of the path predictions. One reason for the decreased accuracy is that the objects or the host vehicle may perform more voluntary corrections under a longer period than a shorter, which corrections may not be accounted for in the path prediction. Early intervention may therefore lead to unnecessary or incorrect intervention. If intervention is made at a late stage, intervention must be made by use of large forces, in the event intervention in the command over the vehicle is performed. On the other hand, if an alarm signal is sent to the driver, correction must be made by the driver by use of large forces. Finally the intervention may be made to late such that it is no longer possible to avoid a particular situation.
Since drivers are constantly adapting to a traffic situation by assessing the situation for following the road, avoiding objects and selecting appropriate speed by accelerating or braking, information about which objects the driver is aware of is a great importance for determining how an active safety system should intervene. Generally intervention by active safety systems is far more accepted by drivers when intervention concerns avoiding objects and situations that the driver was not aware of. For this reason intervention can be allowed at an early stage for objects that the driver was not aware of, while intervention can be made at a late stage for objects that the driver was aware of.
Awareness of an object may be determined by first locating the object by an external object sensor system arranged on a host vehicle. The sensor system determines a direction toward the object. An eye gaze monitor determines the direction of gaze of the driver of the host vehicle. A comparator determines that the driver observes the object if the direction of the gaze of the driver corresponds to the direction toward the object. When having observed the object the driver will be assumed to be aware of the object for a period of time from the time of observation.
The detecting range of commercially available sensor systems for object detection is relatively limited. While it may be possible to detect position and velocity of an object at a relatively large distance, that is around 150 m or more, it is more difficult to determine the type of object at a large distance. A typical value for reliable detection of objects, including detection of position, velocity and type of object, is typically less than 50 m. Traffic scenarios frequently include objects moving at high speed relative to the host vehicle. Vehicles running in the opposite direction of the host vehicle may approach the host vehicle at speeds exceeding 50 m/s relative to the host vehicle under normal circumstances. Considering that traffic scenarios may includes objects moving at high speed relative to the host vehicle, the short detection range of the sensor system makes it difficult to accurately determine whether the driver of the host vehicle is aware of an external object or not, and furthermore makes it difficult to based on determined awareness of the object to separate between early intervention and late intervention of an active safety system.